1. Technical Field of the Invention
The present invention relates to closure caps made of moulded plastics material for closing necked containers and more particularly to closure caps designed to guarantee that the closure that they establish is tamper-proof.
The object of the invention concerns more particularly closure caps made of moulded plastics material of which the guarantee of impregnability is achieved by a ring which extends the base of the skirt of the cap and which is detachable, at least in part, when the container is first opened.
More specifically still, the invention concerns those closure caps which are mounted on the net of a container via helicoidal threads.
2. Description of the Related Art
Tamper-proof closure caps may be classified in two categories.
The first category corresponds to caps provided with a tamper-proof ring which is automatically detached from the base of the skirt upon opening by unscrewing.
In that case, the tamper-proof ring remains in place on the neck of the bottle or container and marks, by its presence, the opening of the cap and consequently the fact that the closure that it effects has been violated.
Such closure caps are satisfactory for the function for which they are designed, and guarantee impregnability of the closure.
However, caps of this first category present a problem for recycling the raw material of the empty containers. As a general rule, it may be assumed that the containers are made of glass or plastics material. On the other hand, the closure caps are mainly made of polypropylene or polyethylene. The caps of the above type therefore leave on the neck of the container a ring of a different material from that of the container. During the recycling operations, it is therefore necessary to sort and separate the two materials present, which presents the problem of the technical means to be employed and of the extra cost added to the recycling process due to the presence of such rings.
The closure caps of moulded plastics material of the second category comprise a tamper-proof ring which must be voluntarily broken and partly detached by the user him/herself.
Such tamper-proof rings are generally of the "pigtail" type, so-called due to the pseudo-helicoidal spiralled shape on the partly trimmed tamper-proof ring which generally remains attached to the skirt of the cap by a connection foot.
The closure caps of this second category achieve the first object of indicating a of violation and solve the subsequent problem of separation, prior to recycling, because the tamper-proof rings remain connected to the caps and are no longer immobilized in the form of belt or ring around the neck of the container.
Although the closure caps of this second category are satisfactory in these two respects, they still raise a problem of manufacture for the following reasons.
The closure caps of the second category may be produced in two ways.
The first consists in moulding on the inner face of the skirt profiles in overthickness of direction parallel to the axis, then in a subsequent take-up operation, forming the transverse plane of rupture between the skirt and the tamper-proof ring, by means of an incision by a cutting blade cutting the whole thickness of the peripheral wall and consequently leaving profiles in internal overthickness.
In this way, the profiles in overthickness constitute cleavable bridges when a force is imposed thereon upon opening via an inner folded band abutting beneath a counter-ring of the neck of the container.
However, for such a tamper-proof ring to be able to perform its function, as provided previously, it is also necessary to arrange in some way or other in the tamper-proof ring and below the transverse plane of rupture, a zone of least resistance on which the user may act voluntarily to provoke the axial opening allowing the ring to be trimmed.
However, such a requirement is not sufficient since, as a general rule, it is also necessary to leave between the ring and the skirt and in the transverse plane of rupture, a non-cutout zone leaving a connection foot to maintain the band cutout, in that case qualified as "pigtail", attached to the cap during the manipulations of opening and reclosing the neck.
The known prior art may be illustrated by Application WO91/17090 and, in particular, by FIGS. 2, 3 and 5 thereof.
As a general rule, these two requirements are satisfied by making, by incision, the transverse cutting plane by means of a knife, of the circular type, presenting in its cutting edge a setback to leave the necessary non-incised part, such a knife comprising, adjacent the setback and in a plane perpendicular to its plane, a rigid blade intended to form the zone of least resistance in the band.
In fact, the above means can only be suitably employed insofar as the intervention of the rigid blade coincides with an interruption of the band folded inwardly and belonging to the tamper-proof belt.
In fact, in the absence of such a coincidence, rupture of the tamper-proof ring becomes impossible.
This is why, during manufacture of such caps, it is necessary to perform, prior to the action of the circular knife, an alignment operation to place the plane of intervention of the blade in alignment or register with that of the interruption of the inner band.
Although this requirement is not insurmountable, it complicates the take-up operation and substantially reduces the production rates for the final cap shaping operation.
The second method of obtaining such caps consists in moulding in the tamper-proof ring a zone of least resistance and in producing or forming the transverse plane of rupture by an incision by means of a circular knife whose cutting edge comprises notches in places to leave cleavable bridges. Such is typically the case of Application WO91/17090.
Such a method is not without interest but it also requires employing a circular knife presenting a setback intended to leave in the transverse plane a non-weakened part in order to form a permanent connection foot between the, "pigtail" band and the skirt.
Consequently, it is also necessary to proceed, prior to the action of the knife, with a relative alignment so that the setback of the blade leaves the non-cutout part of the thickness of the skirt, adjacent to the zone of least resistance
Although the second process is somewhat different from the first, the effect is the same and, as before, it does not enable closure caps to be produced at a very high rate or at least at a rate which is in exact proportion to that of the injection moulding machines.
Furthermore, it is observed fairly frequently that either the opening of the band is produced on the whole turn or this opening is not produced suitably. This is due to the fact that the resistance that the connection foot must offer is inadequate.